I am a developer for only shops but I don't know all about the licence.At first PHP is free, so you can use it. Also HTML and CSS, you doesn't have to use HTML5. For Javascript you should use the ECMAScript so please don't use JQuery or something else and you should make at the bigging the right licence. As CMS you could use OpenCart, it has the GNU GPL License or you could develop an own shop if you have the right PHP skills.
I hope I could help you a bit.
